Separation of molybdenum values from tungsten values by solvent extraction

ABSTRACT

A process for separating molybdate values from tungstate values using solvent extraction is disclosed. The process comprises forming an acidic aqueous feed solution, having a controlled pH, from an impure molybdenum source material containing molybdate and tungstate values by dissolving said source material in an aqueous solution of a mineral acid, contacting said feed solution with a water-insoluble three component organic extractant phase consisting essentially of di-2-ethylhexyl phosphoric acid as an extractant, tributyl phosphate as a solubilizer and a waterinsoluble hydrocarbon solvent, the volumetric ratio of the extractant to the solubilizer being from about 5:6 to about 17:1, the volumetric ratio of the extractant to the solvent being from about 1:1 to about 1:8, the volumetric ratio of the solubilizer to the solvent being from about 1:1 to about 1:17 to extract at least a portion of the molybdate values from said feed solution, separating the resultant aqueous molybdenum-barren phase from the resultant organic molybdenum-pregnant phase, contacting the organic molybdenum-pregnant phase with an aqueous strip solution g ammonium ions, separating the resultant molybdenum-pregnant aqueous strip solution from the resultant molybdenum-barren organic solution and recovering the molybdenum-pregnant, tungsten-free aqueous strip solution.

United States Patent Vincent Cbiola Towanda;

Phyllis R. 00611;, Wysox; Tai K. Kim, Towanda; John A. Powers, New Albany, all

[721 Inventors [54] SEPARATION OF MOLYBDENUM VALUES FROM TUNGSTEN VALUES BY SOLVENT EXTRACTION 10 Claims, No Drawings 521 vs. c1 23/22, 23/51, 23/140, 23/312 ME, 23/23, 23/15 w 511 1-1. c1 c220 59/00, c01 39/00 1501 rm ofstal'dl 23/1s.s, 18-20, 22-24, 51, 312 ME [56] References Cited UNITED STATES PATENTS 3,180,703 4/1965 Ableson et a1. 23/312 ME FOREIGN PATENTS 967,823 8/1964 Great Britain 23/ 155) OTHER REFERENCES Jenkins et a1., Journal of Applied Chemistry, Vol. 14, Oct. 1964, pp. 449-454. 23/155 Primary Examiner-Herbert T. Carter AttorneysNorman J. O'Malley, Donald R. Castle and William McNeilI hydrocarbon solvent, the volumetric ratio of the extractant to the solubilizer being from about 5:6 to about 17:1, the volumetric ratio of the extractant to the solvent being from about 1:1 to about 1:8, the volumetric ratio of the solubilizer to the solvent being from about 1:1 to about 1:17 to extract at least a portion of the molybdate values from said feed solution, separating the resultant aqueous molybdenum-barren phase from the resultant organic molybdenum-pregnant phase, contacting the organic molybdenum-pregnant phase with an aqueous stn'p solution g ammonium ions, separating the resultant molybdenum-pregnant aqueous strip solution from the resultant molybdenum-barren organic solution and recovering the molybdenum-pregnant, tungsten-free aqueous strip solution.

SEPARATION OF MOLYBDENUM VALUES FROM TUNGSTEN VALUES BY SOLVENT EXTRACTION BACKGROUND OF THE INVENTION This invention relates to the recovery and purification of molybdenum from an acidic molybdate solution by a liquidliquid solvent extraction process. More particularly, it relates to th recovery and purification of molybdenum from tungsten-containing molybdenum solutions by a liquid-liquid solvent extraction process wherein molybdenum values are first extracted by an organic mixture and are then recovered as aqueous ammonium molybdate solutions, which are suitable for processing to high-purity ammonium paramolybdate or pure-grade molybdenum trioxide.

Methods for the separation of tungsten and molybdenum are known. In one method, the molybdenum is first reduced with the thio glycolic acid and extracted as molybdenum (V) thiocyanate complex. After reduction with TiCl tungsten is extracted as a tungsten (V) thiocyanate complex. A second method uses tartaric acid as a complexing agent to hold tungsten in solution while molybdenum is precipitated as molybdenum sulfide. In a third method of separation, tungsten is extracted as a tungsten (Vl) 8-hydroxyquinoline complex while the molybdenum remains in the aqueous phase as nonextractable molybdenum (V) ethylenediamine tetraacctic acid complex after reduction with hydrazine hydrochloride.

The disadvantages of the heretofore known process are believed to be apparent. For example, the above-mentioned systems are not suitable for large-scale production. Additionally, in general, molybdenum compounds that are difficult to process further are produced, and in most instances only dilute feed solutions containing molybdenum or tungsten can be used. Ion-exchange separation of, tungsten and molybdenum has also been investigated. In this method molybdenumand tungsten-containing solutions are transferred to a column containing a cation exchange resin. An eluent that is 4M hydrochloric acid and 0.1M citric acid, is used to remove the tungsten, and an eluent that is 1.9M ammonium chloride and 0.44M ammonium citrate is used to remove the molybdenum. Although this method is reported to be quantitative for the separation of tungsten and molybdenum, severalfactors prohibit its use in production, namely, l only very dilute solutions of tungsten and molybdenum can be processed, and (2) the method is time-consuming and results in equipment tie-up.

In copending patent applications Ser. No. 837,777 and Ser. No. 837,925 filed concurrently herewith, there are disclosed methods for purifying molybdenum from certain impurities. Although the molybdenum is purified with respect to impurities such as Cu, Na, K, Fe, etc. the amine extracts both tungsten and molybdenum and a tungsten-free molybdenum product is not obtainable by those methods if tungsten is present as an impurity. It is believed, therefore, that a highly efficient method to produce a tungsten free ammonium molybdate solution from an acidified molybdate solution containing tungsten would be an advancement in the art.

SUMMARY OF THE INVENTION In accordance with one aspect of this invention, an acidic aqueous feed solution having a pH of from about 1 to about 3 is prepared by dissolving a molybdenum source material containing tungsten in an aqueous solution of mineral acid, contacting said aqueous feed solution for a specific time with an organic solution containing di-Z-ethylhexyl phosphoric acid (DZEHPA), tri-n-butyl phosphate (TBP) and a water-insoluble hydrocarbon solvent, where D2EHPA is the extractant, TBP acts as a solubilizer or modifier, and the hydrocarbon is the diluent or solvent, to extract molybdenum into the organic phase, seperating the resultant molybdenum-laden organic solution and the molybdenum-barren aqueous phase, contacting the molybdenum-loaded organic phase with a solution containing a source of ammonium ions to regenerate the or- .ganic phase for recycling, and to produce molybdenum in soluble form suitable for further processing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Any mineral acid can be used to acidify the aqueous feed solution. Sulfuric acid is generally preferred because of its ease of handling, reaction and cost. For example, it is possible to extract molybdenum from acidified molybdate-containing solutions having concentrations as high as l30g./l., (M00 basis) with greater than 99percent efficiency in 4 stages using a 5: lorganic'to aqueous feed solution volumetric ratio.

As previously mentioned, the molybdenum source material contaminated with tungsten, is dissolved in an aqueous solution of a mineral acid. The pH is held at from about lto about 3.0.A higher pH can result in the formation of extractable tungstate species and unextractable molybdenum species .:A lower pH, that is below about 1, can result in degradation'of some of the components of the organic extractant solution and the formation of unextractable molybdenum species. Additionally, lower pH ranges do not advantageously effect the process of this invention and the use of the excess acid merely adds unnecessary costs to the process, therefore, a pH of contain tungsten or the corresponding tungstate. Potassium hydroxide can also be used as the caustic source, however sodium hydroxide is preferred. The process of this invention is independent of the cation portion of the molybdate and tungstate radicals. I

The feed solutions can be relatively concentrated, there'- fore, feed solutions containing as much as 130 g./liter MoO basis can be recovered at greater than 99 percent efficiency; Heretofore, only relatively dilute solutions containing less than about 10 g./liter could be processed by the process known in the prior art.

The organic extractant solution contains di-2-ethylhexyl phosphoric acid, as an extractant, tributyl phosphate as a solubilizer or modifier, and a hydrocarbon solvent as a solvent or diluent.

Although any water-insoluble hydrocarbon solvent, such the petroleum distillate solvents, such as kerosene, naptha,

benzene, toluene and the like can be used as the diluent or 501- vent, kerosene is preferred because of its cost, flash point,'az1cl toxicity rating. As used herein, water-insoluble means thatless than about 5 grams of the hydrocarbon will dissolve in 100 cc. of water at 20 C. These components can be used in various volumetric ratios within specified ranges. The volumetric ratio of extractant to solubilizer can be varied from about 5:6 to about 17:1, the volumetric ratio of extractant to solvent can be varied from about 1:1 to about 1:8 and the volumetric ratio of solubilizer to solvent can be varied from about 1:1 to about 1:17 thus giving the following ranges in the three component system, on a basis of 100, from 1012178 to 48.5:3:48.5 tov 33.3:33.3:33.3. The foregoing ratios are given in terms of extractantzsolubilizerzsolvent solvent respectively.

The extraction of molybdenum from the feed solution into the organic phase occurs rapidly and at least some molybdenum is extracted almost instantaneously, however, for practical design reasons, it is preferred to use longer times so that the systems approach equilibrium. It has been found that from about 20 to 30 minutes of contact time between the organic extractant phase and the aqueous feed solution is preferred.

Shorter periods of contact lower the efficiency and more stages are needed to achieve high efficiencies. Longer periods of contact do not improve the efficiency, therefore lower the.

throughout of the system. The above contact times are based upon using conventional means of agitation that are generally The volumetric ratio of extractant to the feed solution can be varied over a wide range and achieve at least some of the benefits of this invention. As for example, the volumetric ratio of organic extractant to aqueous feed solution can be varied from about 100:1 to about l1l00 and at least some molyb- 5 denum will be extracted. in the instances where maximum l d 1 er nconcentration of molybdenum in the aqueous feed solution is f:. Kd values off an ong co desired, about a 4:l to 6:l organic extraction phase to the ac 5a acid c aqueous feed solution volumetric ratio is preferred. EXAMPLE m Deviations from the preferred ratio can be tolerated but with a 10 corresponding loss in efficiency as is apparent from the Various concentrations of Na,MoO solutions are prepared, detailed examples presented herein. doped with *Mo, acidified to a pH of about 2 with H 80 and In the stripping step the molybdenum-pregnant organic contacted with various phase ratios of organic extractant (23 solution is contacted with an aqueous strip solution containing percent DZEHPA-IO percent TBP-71 percent kerosene). ammonium ions to recover the mol bdenum extracted. Effi- 5 Ali uots of both hases in all sam les are counted and Kds Y q P P cientaqueous solutions contain a source of ammonium ions are obtained. Results appear below. such 'as aqueous solutions of ammonium molybdate, ammonium hydroxide, ammonium chloride and the like. In general, any water-soluble ammonium compound, as well as ammonia, 53mph: Aq, COM phase Ratio m can be used toderive the ammonium ion source, however, a mixture of ammonium molybdate and ammonium hydroxide is 1 M, M003 21 8 883 preferred because of the efficiency, the number of stages 2 69 g./l. Moo, 311 1.37 30.5 required to achieve high recovery and the generation of a strip 2 2 r 8 3f: 3 72 7 solution that can be converted directly into a useable product, 5 so i 3 3 ammonium molybdate. 25 6 so g./l. Moo 511 6.5l 91.0

The period of time required to remove the molybdenum 7 I00 s-l M 006 from the organic phase is generally about the same as for the g :33 mg 2f: 2'3: 2:: removal of molybdenum from the feed solution by the or M 1 game. Deviation from the preferred time results in either i1 130 1. Moo, 5:1 1.99 90.8 lower efficiency or decreased throughput as in the extraction s- 611 (MI 804 step.

The volumetric. ratio of strip solution to the molybdenumpregnant organic phase can be varied f about 00 to At a 5:1 ratio organic to aqueous ratio, a concentration of 130 about 100:1. A volumetric ratio of about I24 to about 4:1 is M002 the feed Solution can be This relatively preferred f an ffi i and Sign standpoint high concentration enables an economic production rate.

To more full illustrate this invention, the followin detailed Y g EXAMPLE iv examples are presented. All parts, proportions, ratios and percentages are on a volumetric basis unless otherwise stated. M l bd l d d organic i contacted with various stripping solutions. Aliquots of both phases in all samples are EXAMPLE I I analyzed and stripping factors and percent stripping obtained Solutions M sodium molybdate are acidified to a pH of from results" about 2 with H 30 and contacted with solutions of DZEH- PA-TBP-kerosene varying in concentration of D2EHPA from 50 percent to 5 percent volumetric basis. Al quots of aqueous 45 Sump", smpping Age, sepamion Sepmfion and organic phases are taken and Kd's (distribution coeffi- Factor cient o/a) obtained. Results of these date are summarized:

1 o.7M Ni-i. ,Mo0. 2.01 66.7 2 i.0M Nii. ,Mno, 40.68 97.6 3 l.SM(NH ),MoO 42.413 97 1 Sample Aq. Soln. Organic Soln Kd 4 2.0M(NH,),M0O, 34.24 97 l 5 05M (NH. ,Moo.+ 68.78 98.5

0.5M NH OH I Na M00 50% EHPA l0% TBP 40% kersoene 52.4

5 Na,Moo, 5% 0212mm 5% TBP 90% kerosene 33.9

EXAMPLE In two stages the 0.5M (NH MoO 0.5M Niipii solution A NazMoo4 Solution is doped with mi idifi d to a H strips greater than about 99.9 percent of the molybdenum in of about 2 with H,SO, and samples are contacted with equal the Organic P volumes of an extractant solution having ratios of 23-6-71 EXAMPLEV DZEHPA-TBP-kerosene. The samples are shaken for. different Periods of from! to 60 minutes- {\Iiquots of t P Molybdenum-loaded organic is contacted with 0.5M samples are counted, Kd's obtained, and optimum contact e 0 d 0 5 -1 0 f times ranging f 1 to 0 Ilme l5 delermmed from the following data: minutes. Aliquots of both phases in all samples are analyzed and stripping coefficients are obtained. The results appear on the following page Sample Contact Time Kd l minv L57 Stripping 2 5 43 Sample Contact Time Coefficient a 10 1.46 4 is 1.56 s 20 1.61 1 1 min. 3.31 6 25 1.9 2 5 84.60 1 30 1.5 3 10 85.08

The above results indicate that some molybdenum is stripped even at one minute contact time with about 25 to about 30 minutes being optimum.

EXAMPLE Vl An aqueous feed containing 130 g./liter of M is tagged with "'W and adjusted to various pHs before it is contacted with 23 percent D2EHPA-6 percent TBP-7l percent kerosene for 25 minutes. Aliquots of both phases from all samples are The results clearly indicate that a pH of at least 2 is preferred in order to maximize the separation of tungsten and molybdenum.

EXAMPLE Vll An organic solution composed of a ratio l:l:l (by volume) DZEPHA-TBP-kerosene is prepared. The aqueous solutions are made by dissolving reagent-grade sodium molybdate in deionized water to give MoO concentrations of 0.5, l, 5, IO, 25 and 50 gmsJl. The pH of the aqueous solutions is adjusted to about 2 using sulfuric acid. The same procedure is followed except that organic composition is 23:6:71 (by volume) D2EPHA TB? and kerosene. Equal volumes of the organic and aqueous solutions are mixed for about 22 inches. When separation is complete a sample of the aqueous solution is analyzed for grams Mo/liter. From this data, the Mo concentration in the organic is determined by difference. The results appear below.

Feed Solution Molybdenum Concentration, (grams/liter) Percentage Molybdenum in Organic Phase Organic Solution EXAMPLE VIII The same procedure is followed as in example Vll except pH of aqueous solution is adjusted to about 2 using HCl and a l :l: l ratio in the organic phase is used. Results appear below.

Feed Solution Molybdenum Concen- Percentage of Molybdenum in tration, (grams/liter) Organic Phase 0 S 99 I 99 5 99 to 99 25 92 50 v 62 The above results indicate that HCl can be used in place of sulfuric acid.

While there has been shown and described what is at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

We claim:

1. A process for separating molybdate values for tungstate values comprising:

a. forming an acidic aqueous feed solution having a pH from about 1 to about 3 by dissolving an impure molybdenum source containing molybdenum and tungsten values in an aqueous solution of a mineral acid;

b. contacting said feed solution with a water-insoluble organic extractant solution consisting essentially of a di-2- ethyl-hexyl phosphoric acid as an extractant, tributyl phosphate as a solubilizer and a water-insoluble hydrocarbon solvent, the volumetric ratio of the extractant to the solubilizer being from about 5:6 to about 17: l the volumetric ratio of extractant to solvent being from about lzl to about l:8 and the volumetric ratio of solubilizer to solvent being from about 1:1 to about 1:17 under temperature conditions not exceeding 45' C., to extract at least a portion of the molybdenum from the feed solution;

c. separating the resultant molybdenum-pregnant organic phase from the resultant molybdenum-barren aqueous phase;

d. contacting said molybdenum-pregnant organic phase with an aqueous strip solution containing ammonium ions to remove at least a portion of the molybdenum-laden aqueous strip solution from the resultant molybdenumbarren organic solution, and

f. recovering the molybdenum-pregnant, tungsten-free strip solution.

2. A process according to claim 1 wherein the pH of said acidic aqueous feed solution is about 2.

3. A process according to claim 2 wherein the volumetric ratio of the organic extractant phase to said acidic aqueous feed solution is from about 4:1 to about 6:1.

4. A process according to claim 3 wherein said hydrocarbon is kerosene.

5. A process according to claim 4 wherein said strip solution is an aqueous solution of ammonium molybdate and ammonium hydroxide.

6. A process according to claim 5 wherein the volumetric ratio of said strip solution to said organic phase is about I .l

7. A process according to claim 6 wherein said molybdenum-barren organic solution is recycled.

8. A process according to claim 2 wherein said process is a batch process.

9. A process according to claim 2 wherein tractant is recycled for use.

10. A process according to claim 9 wherein said process is a continuous process.

the organic ex- 233 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIQN Patent'N o. 3, 1, Dated September 21, 1971 Inventor) Vincent Chiola, Phyllis R. Dodds, Tai K. Kim and John A.

Powers It is certified that error appears in the above-identified patent and that saidLette'rs Patent are hereby corrected as shown below:

Abstract Line 20 "g" should read "containing".

Col. 2, line 68 "throughout" should read "throughput" Col. 4, line 23 "6.88 96.4" should be in two separate columns.

Col. 5. line 45 "inches" should read "minutes" Col. 6, Claim 1 line 24 "Eur" second. instance should read from Col. 6, Claim 1 line 49 et seq. d. and e. mixed up should read d. contacting said molybdenum-pregnant organic phase with an aqueous strip solution containing ammonium ions to remove at least a portion of the molybdenum from the organic phase,

e. separating the resultant molybdenumladen aqueous strip solution from the resultant molybdenum-barren organic solution, and

Signed and sealed this 11th day of April 1972.

(SEAL) lttest:

BDWAR1J M.FLETQHER,JR. ROBERT GOT'I'SCHALK rttestlng Officer Commissioner of Patents 

2. A process according to claim 1 wherein the pH of said acidic aqueous feed solution is about
 2. 3. A process according to claim 2 wherein the volumetric ratio of the organic extractant phase to said acidic aqueous feed solution is from about 4:1 to about 6:1.
 4. A process according to claim 3 wherein said hydrocarbon is kerosene.
 5. A process according to claim 4 wherein said strip solution is an aqueous solution of ammonium molybdate and ammonium hydroxide.
 6. A process according to claim 5 wherein the volumetric ratio of said strip solution to said organic phase is about 1:1.
 7. A process according to claim 6 wherein said molybdenum-barren organic solution is recycled.
 8. A process according to claim 2 wherein said process is a batch process.
 9. A process according to claim 2 wherein the organic extractant is recycled for use.
 10. A process according to claim 9 wherein said process is a continuous process. 